It's not a honeymoon phase. It's scale and preserving experience. The first reactors built in the 1950s we're actually pretty bad on a dollar to power ratio. But experience and economies of scale drove prices down in the 1960s and 1970s. When you contract for a limited run of, say, 4 steam generators [1] it's more expensive than a run of 80 of them. Nuclear plants in this period averaged ~2 billion dollars per gigawatt of capacity (and remember that's at a >90% capacity factor).

1. https://en.m.wikipedia.org/wiki/Steam_generator_(nuclear_pow...